1. Field of the Invention
The present invention relates to a magnetoresistance effect type head used as for example a reproducing head of a magnetic disk unit and a magnetic recording/reproducing head system therewith.
2. Description of the Related Art
In recent years, as needs of high density magnetic recording units are becoming strong, a hard disk type magnetic recording/reproducing head system having a reproducing head composed of a shield type magnetoresistance effect type head (hereinafter referred to as an MR type head) and a recording head composed of an induction type magnetic head has been developed. In addition, as an MR device, a giant magnetoresistance effect due to a spin dependent scattering effect was discovered. For example, an MR head composed of a spin valve film or an artificial lattice film has been experimentally used as a reproducing head.
In the above-described magnetic recording/reproducing head system, due to the flatness and fabrication process required for the reproducing head, a structure of which a recording head is formed above the reproducing head has been used. In this case, leads that supply a current to the reproducing head are composed of a conductor film with a thickness of around 100 to 300 nm. In addition, from a view point of S/N ratio, a structure of which the track width of the reproducing head is smaller than the track width of the recording head is conventionally used. The track distance of the reproducing track is conventionally defined by the width between the leads.
FIG. 18 is a sectional view showing a structure of a magnetic recording/reproducing head system having a conventional shield type MR head. Next, with reference to FIG. 18, a fabrication process of a conventional head will be described. A CoZrNb alloy film with a thickness of around 1.5 .mu.m is formed as a lower shield layer 1 on a substrate (not shown) by the spattering method. The resultant structure is patterned in a shield shape by the ion etching method. An .alpha.Al.sub.2 O.sub.3 film is formed as a lower reproducing gap 2 for a thickness of around 150 nm. A single film that has the MR effect or a laminate film (MR film) 3 is formed for a thickness of around 40 nm on the resultant structure and patterned in a stripe shape.
A Cu film or the like is formed as leads 4 for a thickness of around 100 nm on the stripe shaped MR film 3. A resist is coated on the resultant structure corresponding to the shape of the leads and then baked at a relatively high temperature. An ion beam is injected into the substrate with an angle so as to pattern the leads 4. The edge portions of the leads 4 are tapered so as to securely insulate the leads 4 and an upper shield layer. Thus, the film thickness of the leads gradually decreases. The distance between the tapered leads 4 becomes a reproducing track (T.sub.R), namely, a signal detecting area.
An .alpha.-Al.sub.2 O.sub.3 film is formed for a thickness of around 150 nm as an upper reproducing gap 5 and then patterned by the lift-off method. A CoZrNb alloy film is formed for a thickness of around 3 .mu.m as a lower recording magnetic layer 6 that also functions as the upper shield layer and then patterned by the ion etching method. An .alpha.Al.sub.2 O.sub.3 film is formed for a thickness of around 200 nm as a recording gap 7. A coil (not shown) is formed and then insulated. A CoZrNb alloy film is formed for a thickness of around 4 .mu.m as an upper recording magnetic layer 8 and then patterned. In this example, a portion formed opposite to the lower recording magnetic layer 6 through the recording gap 7 of the upper recording magnetic layer 8 becomes a recording track (T.sub.W). Thus, by the above-described fabrication process, a magnetic recording/reproducing head system of which a recording head is separated from a reproducing head is obtained.
The high record density of the magnetic recording/reproducing head system can be accomplished by narrowing the track width and the gap of the reproducing head. However, in the conventional head structure and fabrication process thereof shown in FIG. 18, there are various problems. In a structure of which the track width is narrowed, the following problem takes place. In the conventional magnetic recording/reproducing head system, the reproducing track T.sub.R is defined by the gap of the leads 4 and the width of the recording track T.sub.W is larger than the width of the reproducing track. In this case, the irregularity of the leads 4 for a thickness of around 100 nm are transferred to the upper reproducing gap 5, the upper shield layer/lower recording magnetic layer 6. Thus, the irregularity for a thickness of around 100 nm are formed in the vicinity of the edge portions of the recording track T.sub.W.
To accomplish a high record density, as the track width decreases, the large irregularity in the vicinity of the edge portions of the track cause a recording fringe. In other words, when the track width is in the range from around 1 to 2 .mu.m, the ratio of the protrusion portions and recess portions of the track edges in the record track width increases. Thus, a distorted area of the recorded medium magnetizing pattern increases and thereby the reproduced output decreases. On the other hand, in a structure of which the reproducing track is narrowed, the following problem takes place. Since the MR film 3 that overlays with the leads 4 also read information from the medium as well as the MR film 3 corresponding to the track portion, off-track characteristics deteriorate and the influence of the reproducing fringe becomes large.
On the other hand, in a structure of which the gap is narrowed as shown in FIG. 18, the tapers at the edge portions of the leads 4 are important to securely insulate the upper shield layer 6 from the leads 4. To gradually taper the edge portions of the leads 4, when the leads are formed by the ion etching method, the resist should be baked at a high temperature so as to taper the resist. Alternatively, when the MR film 3 is composed of a laminate film, the etching operation should be strictly controlled because the MR film 3 cannot be excessively etched. However, when the resist is baked at a high temperature, the interfacial diffusion takes place in the laminate film and thereby the resistance variation ratio decreases. When the resist is removed with an alkaline solution after the ion etching process is performed, the alkaline solution may corrode the laminate film (for example, a spin valve film). In addition, due to the deviation of the operation of the etching unit, the yield in the fabrication process for forming the leads 4 decreases.
Moreover, in the case of a spin valve film as a laminate film that has the giant magnetoresistance effect, an antiferromagnetic film composed of for example FeMn is normally formed above the spin valve film due to the crystalline orientation. In this case, since the antiferromagnetic film, a magnetic film in the spin valve film that exchange-bonds with the antiferromagnetic film, and a non-magnetic film composed of for example Cu are magnetically insensible, they function as an upper gap. When a conductive protection film is formed on the spin valve film, they function as a gap. Thus, the thickness of the insulation film as the upper gap becomes the difference between the designed gap length and the thickness of the portion that functions as the gap. Consequently, the thickness of the insulation film that is formed at the taper portions further decreases. As a result, the yield of the insulation further decreases.
Besides the structure of which the leads are formed above the MR film as shown in FIG. 18, other structures have been disclosed. In related art references as Japanese Patent Laid-Open Publication Nos. 3-283477 and 4-161874, leads are formed below an MR film. Alternatively, as another related art reference as Japanese Patent Laid-Open Publication No. 6-267030, leads are disposed below and above an MR film. In these structures, the MR film is formed on a flat base. However, when leads are formed above and below the MR film, irregularity of the leads are transferred to the upper shield layer. Thus, as with the structure of which the leads are formed above the MR film, in a structure of which the track and/or gap is narrowed, various problems take place. In addition, when the spin valve film is used, an antiferromagnetic film composed of for example FeMn for fixing the magnetization is formed above the spin valve film so as to obtain excellent characteristics. However, when leads are formed above the MR film, since a sense current flows at the interface between the antiferromagnetic film and the magnetic film, due to the influence of the electric field, heat, and so forth, the reliability of the magnetic fixation at the interface deteriorates. Thus, the structure of which leads are formed below the MR film is more advantageous over the structure of which the leads are formed above the MR film.
However, in the conventional head structure of which the leads are formed below the MR film, the following problem takes place. In the related art reference as Japanese Patent Laid-Open Publication No. 4-161874, an MR head of which the contacted surfaces of a pair of leads, an insulation film, and an MR film (the insulation film and the MR film are disposed between the leads) are flatly formed is described. In the related art reference as Japanese Patent Laid-Open Publication No. 3-283477, an MR head of which a flat MR film is formed on leads in parallel with a substrate is described. In the structure of which the leads are formed below the MR film, although a recording fringe of the recording head is prevented, when the reproducing track width is narrowed to around 1 to 2 .mu.m for a high record density, the MR film corresponding to the leads also reads a signal from the medium and the influence of the reproducing fringe results in. In the head structures of the above-described related art references, the etch-back process or a combination of the bias-spatter process and the etch-back process is used to flatten the leads and the insulation layer formed therebetween. Thus, a much strict process control is required as a fabrication method. Thus, the yield of the fabrication will decrease.
As described above, in the conventional MR head of which the leads are formed above the MR film, when the track width is narrowed for a high record density, irregularity of the lead portion are transferred to portions in the vicinity of the edge portions of the recording track. The variation of the recording gap results in a recording fringe. In addition, a signal reproduced from the MR film that overlays with the leads are superimposed with a reproduced output signal, resulting in a reproducing fringe. Moreover, in a structure of which the gap is narrowed, a short-circuit takes place between the leads and the upper shield layer. This problem is especially remarkable when an MR film composed of a laminate film as a spin valve film or the like is used.
On the other hand, in the conventional structure of which the leads are formed below the MR film, although the recording fringe is suppressed, a signal read from the MR film that overlays with the leads cannot be suppressed. Thus, the reproducing fringe cannot be decreased. In addition, since the fabrication process should be strictly controlled, the yield of the fabrication tends to decrease.